On August 8, 1846, President Polk submitted a message to Congress asking for $2 million to ease future boundary negotiations between the United States and Mexico—the former “ought to pay a fair equivalent for any concessions which may be made by Mexico.” The House agreed to take up such an appropriations bill after a two-hour recess. During the interim, a group of Northern antislavery Democrats (most notably New York’s Preston King, and including Pennsylvania’s David Wilmot) huddled together and produced this little piece of dynamite:
Provided that, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico, by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the monies herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime whereof the party shall be first duly convicted.
Wilmot introduced the proviso (hence its well-known name), but Jacob Brinkerhoff of Ohio later claimed to have written it. Wilmot was an unlikely candidate to have initiated such a battle—he was a vocal states’ rights Democrat who believed Congress had no power to interfere with slavery in states where it already existed (unlike abolitionists, who often relied on the Guarantee Clause of Article IV, Section 4 to come to the opposite conclusion). His free-soil philosophy had explicitly racist underpinnings: “I would preserve for free white labor a fair country . . . where the sons of toil, of my own race and own color, can live without the disgrace which association with negro slavery brings upon free labor.” He’d voted for the annexation of Texas as a slave state, been the only Pennsylvanian to have voted for Polk’s tariff reduction, and supported the Administration on Mexican War matters up until now.
The Wilmot Proviso failed in the Senate but significantly altered the tenor of Congressional and national discussion about how the Mexican War ought to be concluded. Thomas Hart Benton later wrote that the Proviso “was nugatory and could answer no purpose but that of bringing on a slavery agitation,” as no major figure had yet advocated the introduction of slavery into areas that seemed naturally inhospitable to it. “Never were two parties so completely at loggerheads about nothing.” Polk denounced Wilmot’s “mischievous and foolish” maneuver in his diary: “What connection slavery had with making peace with Mexico it is difficult to conceive.” Widespread realization of that connection may have been strategically troublesome for Polk, but the connection certainly existed, and its consequences were here to stay. Votes on the Wilmot Proviso reflected (and probably sharpened) a trend toward the primacy of sectional identity over partisan affiliation in Congressional voting behavior, with disturbing implications for what national politics remained before our ancestors started killing each other.
Wilmot’s language on the non-extension of slavery closely tracked that of the Northwest Ordinance of 1787, which provided that “[t]here shall be neither slavery nor involuntary servitude in the said territory, otherwise than in the punishment of crimes whereof the party shall have been duly convicted.” The more familiar Thirteenth Amendment also followed this general formulation.
I copied the text in the beautiful block quotes above straight from the actual Proviso, not from a published “primary” source. In many of those sources, “monies” is spelled “moneys,” “be first” is rendered “first be,” “Republic” isn’t capitalized, and the comma after “Mexico” is omitted. And in case you didn’t notice, Wilmot’s name is misspelled at the bottom of the actual Wilmot Privoso. I like it when history is hilarious.
As a side note, I can claim to own something else Wilmot wrote: